Blood Collection in Rabbits

Video

Video created and narrated by Dr. M. Scott Echols. Video script adapted by Dr. Christal Pollock from Venipuncture in Small Mammals, an article co-authored by Jody Nugent-Deal and C. Pollock.

 

Introduction

Rabbits (Oryctolagus cuniculus) are prey species that are easily stressed in a hospital setting. Make every effort to keep all interactions as calm and quiet as possible. Consider sedation (midazolam 0.25-1.0 mg/kg IM) or general anesthesia, using isoflurane or sevoflurane, to minimize the stress of restraint, particularly if handler or phlebotomist are relatively inexperienced. Application of a topical anesthetic such as EMLA© cream (AstraZeneca LP, Wilmington, DE) over the vein 30 minutes prior to venipuncture can also prove helpful. Remember that EMLA must be covered with a semi-occlusive dressing to work appropriately.

 

Equipment

The rabbit has a relatively short prothrombin time and whole blood quickly clots at room temperature. To minimize the risk of clot formation, it can be helpful to pre-heparinize the needle and syringe by drawing heparin into the needle and expelling the excess from the hub. Always check with your lab first since heparin can cause changes in staining quality.

To collect blood from a rabbit, attach a 22- to 27-gauge needle to either a 1, 3, or 6-ml syringe. Place blood samples into microtainers (BD Microtainer Blood Collection Tubes; Becton Dickinson and Company, Franklin Lakes, NJ).

The total volume of blood that can be safely collected typically ranges from 0.5% to 1.0% body weight (BW). Collect smaller volumes (0.5% BW) from geriatric patients or those suspected to have anemia or hypoproteinemia. For example, a maximum volume of 5.0-10.0 ml of blood may be collected from a 1000-gram rabbit.

 

Recommended venipuncture sites

Jugular vein

The jugular vein is the most popular site for blood collection in the rabbit. Restrain patients in dorsal or lateral recumbency with the head extended and the legs pulled down toward the body. Rabbits may also be held in sternal recumbency at the edge of an exam table like a cat (Fig 1). Take care not to overextend the head and neck. Jugular venipuncture may be particularly challenging in obese rabbits or does with a large dewlap as it can be difficult to visualize the vessel. Clipping can improve visibility, but take care not to damage the delicate skin. Insert the needle bevel up, and collect your sample. Afterwards gently remove the needle, and apply firm, steady pressure.

 Jugular venipuncture in a  held in sternal recumbencyrabbit

Figure 1. Jugular venipuncture in a rabbit (Oryctolagus cuniculus) held in sternal recumbency. Click image to enlarge.

Lateral saphenous vein

Another common site for blood collection is the lateral saphenous vein (Fig 2). Although the rabbit can be conscious, until you are experienced in rabbit restraint it is preferable that the rabbit be sedated or anesthetized because of the danger of kicking and subsequent back or leg injury.

The lateral saphenous vein is another popular venipuncture site in the rabbit.

Figure 2. The lateral saphenous vein is another popular venipuncture site in the rabbit. Click image to enlarge.

Place the rabbit in sternal or lateral recumbency. Wrapping the rabbit’s rump and bottom leg in a towel can minimize the risk of kicking. Another technique that can be used in the conscious patient is to slide the entire hind end towards the edge of the table, allowing the hind limb to drop off the table (Fig 3). This allows access to the limb without placing any torque on the hindquarter. Grasp the upper leg just above the stifle to engorge the vessel and prevent the limb from moving (Fig 4).

Pulling the towel forward allows the hindquarter to drop off the table’s edge.

Figure 3. Pulling the towel forward allows the hindquarter to drop off the table’s edge. Click image to enlarge.

Grasp the limb just above the stifle to immobilize the leg and engorge the vessel.

Figure 4. Grasp the limb just above the stifle to immobilize the leg and engorge the vessel. Click image to enlarge.

Alternative sites

Less common venipuncture sites in the rabbit include the marginal ear vein and cephalic vein.

Cephalic vein

Whenever possible, reserve the cephalic vein for intravenous catheter placement. If you elect to use the cephalic vein, it is particularly important to apply a local anesthetic beforehand since the rabbit is very likely to move its leg otherwise.

 

Ear vessels

Ear vessel venipuncture in the pet rabbit is somewhat controversial. Some clinicians only use the ear as a last resort. Rabbit vessels are fragile, and even a mild ear hematoma or bruising may be unacceptable to some owners. Disruption of blood flow in the ear can also potentially lead to thrombosis, ischemia, and sloughing of pinnal tissue (fig 5).

 Ear venipuncture can potentially lead to clot formation and ischemic necrosis of pinnal tissue

Figure 5. Ear venipuncture can potentially lead to clot formation and ischemic necrosis of pinnal tissue. Click image to enlarge.

Nevertheless even with significant hematoma formation, the incidence of clinical problems is rare, perhaps because the rabbit pinna has significant collateral circulation(Fig 6).

 The normal rabbit ear possesses significant collateral circulation.

Figure 6. The normal rabbit ear possesses significant collateral circulation. Click image to enlarge.

The central ear artery and marginal ear vein are also readily accessible (Fig 7, Fig 8). Most rabbits seem to be more stressed by manual restraint than cannulation of the ear vessel, therefore the ear can be a good choice for a high-strung, nervous individual.

The central ear artery and marginal auricular vein are readily accessible.

Figure 7. The central ear artery and marginal auricular vein are readily accessible. Click image to enlarge.

Cannulation of the marginal ear vein.

Figure 8. Cannulation of the marginal ear vein. Click image to enlarge.

  • Restrain the rabbit in sternal recumbency. Wrap the animal in a large towel to prevent movement.
  • Carefully shave fur or apply alcohol over the vessel to improve visualization.
    It can also help to warm the vessel by gently stroking and tapping the ear or by applying a warm, moist gauze 4-x-4 for a few minutes.
  • Select a 21 to 23-gauge needle or butterfly catheter in large or medium-sized rabbits. Use a 23 or 25-gauge needle for small rabbits.
  • Multiple techniques have been described for ear vessel cannulation. Some prefer to use a needle or butterfly catheter alone, catching blood in an appropriate collection tube.
  • Direct the needle toward the base of the ear, with the insertion point closer to the tip of the ear. Applying tension to the ear will improve the ease of needle insertion (Fig 9). To minimize the risk of hematoma formation, first insert the needle parallel to the artery. Once the needle is in the subcutaneous space, then direct the needle into the vessel.

    Direct the needle toward the ear base while applying tension to the pinna.

    Figure 9. Direct the needle toward the ear base while applying tension to the pinna. Click image to enlarge.

  • When using a syringe it is important not to apply too much negative pressure (Fig 10). If the vessel collapses during blood collection, gently stroke the ear until the vessel relaxes and blood begins to flow again.

    Use of a butterfly catheter reduces negative pressure placed on the vessel.

    Figure 10. Use of a butterfly catheter reduces negative pressure placed on the vessel. Click image to enlarge.

  • Afterwards, apply pressure over the collection site for an extended period to ensure adequate hemostasis and to minimize the risk of hematoma formation.

References